This invention relates to removal of magnetic developing material from a developed, magnetically latently imaged member; and, more particularly to the removal of magnetic developing material from background areas of the member.
Latently imaged members such as, for example, electrostatically latently imaged xerographic photoconductive members and latently magnetically imaged magnetographic imaging members are typically developed by deposition of developer material on the imaging member. In magnetic imaging the developing material is magnetic and attracted by magnetic fields to the latent magnetic image created in a magnetizable imaging member such as, for example, ordinary magnetic recording tape. In electrostatographic imaging systems such as, for example, xerography, the developing material typically comprises the two components of carrier and toner. The toner material is typically capable of becoming triboelectrically charged and, owing to this charge is attracted to the charge pattern residing on the photoconductive imaging member. In either case, as a practical matter, developer material is attracted to and deposited upon the imaging member not only in imagewise configuration in areas of the member corresponding to the latent image but also is deposited upon non-image areas of the imaging member.
These non-image or background areas of the imaging member which bear developing material will transfer these developer materials to the copy medium employed during transfer of the imagewise configured deposition of developing material to the copy medium. Such transfer results in reduced contrast between the transferred image and copy medium and is, therefore, generally undesirable.
Further, in developing latent magnetic images on a magnetizable member it is necessary due to the short range nature of magnetic forces (rapid decrease with distance) to introduce the developing material within a very short distance from the latent magnetic image, typically within about 10 microns of the image, to ensure development of the latent image. This extremely close proximity generally means that developing material will deposit on background areas.
The desirability of removing excessive xerographic developing material is well known and recognized in the xerographic art; and is indicated on the magnetic imaging art such as, for example, in U.S. Pat. No. 3,120,806 wherein direct flood developing of the copy medium under the influence of, but out of contact with the latent magnetic image, is followed with air-knife removal of excessive developing material.
While vacuum removal means are disclosed in the xerographic art for the purpose of removing powder clouds of xerographic developer from machine cavities, I am unaware of any vacuum removal means designed to operate directly upon the developed, latently imaged member in either the xerographic or magnetic imaging art for the purpose of removing developer material directly from background areas of the imaging member (i.e., photoconductor or magnetic tape).
In new and growing areas of technology, new methods, apparatus, compositions, and articles of manufacture are often provided in order to practice the new and growing area of technology in a new mode. The present invention relates to a new and advantageous vacuum removal means for directly removing magnetic developer material from background portions of a developed, latently magnetically imaged member.